Proposed model of major sequential biochemical events of a trophic response

Cell-autonomous circadian clock of hepatocytes drives rhythms in transcription and polyamine synthesis

The circadian clock generates daily rhythms in mammalian liver processes, such as glucose and lipid homeostasis, xenobiotic metabolism, and regeneration. The mechanisms governing these rhythms are not well understood, particularly the distinct contributions of the cell-autonomous clock and central pacemaker to rhythmic liver physiology. Through microarray expression profiling in Met murine hepatocytes (MMH)-D3, we identified over 1,000 transcripts that exhibit circadian oscillations, demonstrating that the cell-autonomous clock can drive many rhythms, and that MMH-D3 is a valid circadian model system. The genes represented by these circadian transcripts displayed both cophasic and antiphasic organization within a protein-protein interaction network, suggesting the existence of competition for binding sites or partners by genes of disparate transcriptional phases. Multiple pathways displayed enrichment in MMH-D3 circadian transcripts, including the polyamine synthesis module of the glutathione metabolic pathway. The polyamine synthesis module, which is highly associated with cell proliferation and whose products are required for initiation of liver regeneration, includes enzymes whose transcripts exhibit circadian oscillations, such as ornithine decarboxylase and spermidine synthase. Metabolic profiling revealed that the enzymatic product of spermidine synthase, spermidine, cycles as well. Thus, the cell-autonomous hepatocyte clock can drive a significant amount of transcriptional rhythms and orchestrate physiologically relevant modules such as polyamine synthesis.

Liver regeneration: methods for monitoring and their applications

Liver regeneration is an essential component of the reparative process following liver injury and surgical resection. It can be assessed by different tissue-based tests such as liver weights, mitotic counts, DNA contents and synthesis rates, immunohistochemical staining of nuclear antigens, gene expressions and certain protein levels or various serum-based tests that largely consist of specific enzyme determinations or documentation of certain proliferation markers. Although the simplest tissue-based test of liver regeneration is measurement of liver weights, these determinations are influenced by the extent of deposition of various materials not directly related to regeneration, such as lipids, glycogen and blood volumes. Because mitosis constitutes a very short segment of the cell cycle, mitotic counts are infrequently observed by light microscopy. Thymidine and BrdU incorporation into DNA are the reference tools for studying DNA synthesis, but their use requires pre-injection with radioactive isotopes or nucleotides which render them impractical for human studies. Flow cytometry is an accurate and objective method of monitoring hepatic regenerative activity but requires sophisticated equipment that is not generally available in many laboratories. Immunohistochemical staining for nuclear antigens (Ki-67, proliferating cell nuclear antigen [PCNA], DNA polymerase alpha and nucleolar organizer region [NOR] proteins) are acceptable and commonly used methods of monitoring regenerative activity but are subject to inter- and intra-observer variability. Gene expression rates such as Histone-3 mRNA abundance are hampered by the relatively low rates of gene transcription and the need for recombinant DNA technology. Protein and enzyme levels in liver tissues, such as putrescine, ornithine decarboxylase and thymidine kinase, are not precise and are confounded by the nutritional status of the host. While PCNA protein levels measured by immunoblot hold promise as a simple, accurate and reproducible marker of liver regeneration, additional studies are required to determine if this is a valid marker of regenerative activity in various models of hepatic injury and in humans. Of the serum-based determinations: thymidine kinase, ornithine decarboxylase, fibronectin, alpha fetoprotein, and early pregnancy factor offer practical and non-invasive tools to monitor liver regeneration, but the sensitivity and specificity of these tests have yet to be determined. In conclusion, many tissue and serum-based methods have been employed in clinical and experimental studies to assess liver regeneration; however, a gold standard has yet to be identified. Because of the disadvantages inherent in each method, and until a new, more accurate marker is identified, clinicians and scientists should incorporate a minimum of two independent markers in studies of liver regeneration.

Quantification and localization of ornithine decarboxylase in the embryonic palate

Ornithine decarboxylase (ODC; EC4.1.1.17), the key enzyme in polyamine biosynthesis, and intracellular polyamines increase rapidly and markedly in tissues and cells that are actively proliferating as well as differentiating and decrease as these processes cease. ODC activity has also been implicated as playing a role in the proliferation and differentiation of cells derived from the developing palate. Ornithine decarboxylase activity was thus quantified and ODC localized in the developing murine palate in vivo. Levels of ODC activity showed little variation during the ontogeny of the palate, averaging 126 pmol CO2/mg protein/hr. When difluoromethylornithine (DFMO), an irreversible inhibitor of ODC activity, was administered to pregnant mice throughout the period of palate development (days 11-14), palatal tissue ODC activity was reduced by 85%. No craniofacial malformations were observed, however. The lack of a teratogenic effect by DFMO treatment could be due to sufficient remaining ODC activity in craniofacial tissue and/or maintenance of intracellular polyamine levels by the activity of a polyamine transport system. The activity of this system was demonstrated by the ability of palatal tissue in vivo to take up radiolabeled putrescine. The presence of a polyamine transport system was previously suggested by the demonstration of such a system in palate mesenchymal cells in vitro. Dramatic temporal and spatial shifts in tissue patterns of immunolocalization for ODC in developing palatal tissue were also seen. Immunostaining for ODC was evenly distributed in oral, nasal, and medial edge palate epithelial cells on day 12 of gestation. The basal aspects of epithelial cells were, however, more intensely stained. Mesenchymal cells exhibited a peri-nuclear immunostaining pattern. On days 12 and 13 of gestation, the staining patterns for ODC in palate epithelial and mesenchymal cells were comparable. On day 14 of gestation, all regions of the palate epithelium, particularly the medial edge epithelia, were immunostained for ODC, whereas the intensity of staining in the mesenchymal cells was significantly reduced. This study represents essential initial observations toward understanding the role that ODC may play in normal craniofacial development.

Role of polyamine in the regulation of RNA synthesis in uterine nucleoli

Administration of estradiol (E2) to ovariectomized mature rats has been shown to result in synthesis of uterine polyamines in the same temporal manner as E2 regulation of nucleolar transcription. Data is presented on the in vivo and in vitro effects of polyamines on uterine nucleolar RNA synthesis. Transcervical intrauterine administration of putrescine (100 micrograms), spermidine (100 micrograms), or spermine (100 micrograms) resulted in an increased transcriptional activity of 93 and 82% in uterine nucleoli isolated from putrescine and spermidine treated animals, respectively. Spermine administration was without effect on uterine nucleolar transcription. The polyamine-induced increase in transcription was totally accounted for by an increased rate of elongation of previously initiated RNA chains. No effect on the number of nucleolar RNA chains in the act of synthesis was observed. Preincubation of uterine nucleoli, isolated from control animals (no E2) with putrescine, spermidine, or spermine in the presence, but not in the absence of ATP, resulted in 44, 83 and 31% increased nucleolar RNA synthesis, respectively. In vitro polyamine-induced nucleolar RNA synthesis was correlated with a polyamine activated phosphorylation of nucleolar proteins of 110,000 24,000, 18,000 and 14,000 Da. Results suggest that early E2 action may result in activation of the polyamine pathway which modulates nucleolar protein kinase activity; initiating an increase in nucleolar transcription.

Perturbations in polyamines and related enzymes following chlordecone-potentiated bromotrichloromethane hepatotoxicity

The mechanism by which chlordecone (CD) amplifies the hepatotoxicity of halomethanes such as CCl4, CHCl3, and BrCCl3 has been a subject of intense study. Recent work has shown that suppression of hepatocellular regeneration leads to accelerated progression of liver injury leading to complete hepatic failure due to an unusual interaction between individually nontoxic low-dose combination of CD and CCl4. Since polyamines are involved in cell division, their levels reflect the extent to which there is suppression of hepatocellular regeneration during CD and CCl4 interaction. The present studies were designed to investigate the polyamine levels and associated enzymes in livers of rats treated with BrCCl3 alone or CD and BrCCl3 low-dose combination in order to confirm whether the sequence of events of hepatotoxicity is similar to that seen in CCl4 toxicity or that seen during CD and CCl4 interaction. The extent of liver toxicity in rats fed 10 ppm chlordecone (CD) for 15 days prior to the injection of a single low dose of BrCCl3 (15 microL/kg body weight) or after exposure to a high dose of BrCCl3 (80 microL/kg body weight) without CD pretreatment, was similar 6 and 24 hr later as assessed by plasma transaminase levels. There was also an increase in transaminase levels, in rats exposed to a single low dose of BrCCl3 alone (15 microL/kg body weight) but this increase was far below the high-dose exposure alone or the combination treatment. Hepatic levels of ornithine decarboxylase, S-adenosylmethionine decarboxylase, N1-acetylputrescine, N1-acetylspermidine, putrescine, spermidine, and spermine at the end of 24 hr increased after exposure to a low dose of BrCCl3 alone as compared to exposure to a high dose alone or the low-dose combination of CD and BrCCl3. Liver spermidine N1-acetyltransferase was elevated at 2, 6, and 24 hr after exposure to a high dose of BrCCl3 alone as compared to treatment with a low-dose combination of CD and BrCCl3 suggesting decreased synthesis of this enzyme, in spite of a greater need as seen from liver transaminase levels. In general, it was observed that there is significant elevation in some polyamines and related enzymes during toxicity of a low dose of BrCCl3 which seemed to stabilize within 24 hr. This was not observed with the other two groups of rats exposed either to BrCCl3 high dose alone or the low-dose combination of CD and BrCCl3.(ABSTRACT TRUNCATED AT 400 WORDS)

Suppression of lymphocyte proliferation by hexamethylene diamine

The antiproliferative potential of hexamethylene diamine (HMDA) for mitogen-stimulated splenic lymphocytes was evaluated in vitro at final concentrations of 0.1-16 mM. Addition at the start of culture or after 24 or 48 h of culture decreased the proliferative response to T and B cell mitogens. However, the concentration of HMDA required to cause suppression increased with incubation time. Removal of diamine after 24 h allowed cells to proliferate normally upon reculture with mitogen. Mitogenic responses of cultures containing the potent ornithine decarboxylase (ODC) inhibitor alpha-difluoromethylornithine (DFMO) were also inhibited in a time and dose dependent fashion. ODC activity, which was much greater in cultures stimulated with Con A than LPS, was markedly decreased by inclusion of diamine or DFMO in the culture medium. Addition of putrescine to cultures did not reverse the suppressive effects of diamine on proliferation but did restore DFMO-containing cultures to control levels of activity. These results indicate that HMDA does suppress lymphocyte proliferation in vitro by alteration of ODC and polyamine activity. However, comparison of results obtained with DFMO and HMDA suggests that HMDA may act via multiple pathways, only one of which involves inhibition of ODC activity.

Hepatic polyamines and related enzymes following chlordecone-potentiated carbon tetrachloride toxicity in rats

Chlordecone potentiation of the hepatotoxic and lethal effects of CCL4 has been well established. Recent studies have shown that the suppression of hepatocellular regeneration results in an accelerated progression of liver injury leading to complete hepatic failure. Since polyamines are involved in cell division, these studies were designed to investigate the polyamine levels and associated enzymes in the livers of rats treated with a low-dose combination of CD and CCl4. For comparison, a large toxic dose of CCl4 was also employed. The extent of liver toxicity in rats fed 10 parts per million chlordecone (CD) for 15 days and subsequently injected with a single dose of CCl4 (100 microL/kg body weight) or a high dose of CCL4 alone (2.5 mL/kg body weight) was similar 6 and 24 hr later as assessed by plasma transaminase levels. There was significant elevation in liver ornithine decarboxylase, S-adenosylmethionine decarboxylase, and putrescine at 24 hr and spermidine N1-acetyltransferase, N1-acetylputrescine, putreanine, putrescine, and N1-acetylspermidine at 6 hr in rats treated with the high dose of CCl4 alone compared to the combination treatment. Spermidine levels decreased up to 6 hr and then increased up to 24 hr for both treatments. Spermine continuously decreased up to 24 hr for the CD and CCl4 low-dose combination treatment compared to rats treated with a high dose of CCl4 alone. Spermidine levels were lower than in controls and rose towards control value between 6 and 24 hr after the combination treatment and the high dose of CCl4. Results indicate that the CD and CCl4 low-dose combination treatment increased liver toxicity, resulting in compromised polyamine metabolism that is coincidental with suppressed hepatocellular regeneration, which leads to an accelerated progressive phase of liver injury and culminates in complete hepatic failure.

Effect of methotrexate on the intestinal mucosa of PGE2-treated rats

In the present study, we aimed to protect the intestinal mucosa from small bowel damage in methotrexate (MTX)-treated rats. The protective effect of prostaglandin E2 (PGE2) was investigated. Ileal integrity was evaluated making use of different biochemical parameters: content of sucrase and maltase activities, contents of DNA, proteins, AMPc, PGE2, putrescine (Put), spermine (Spm) and spermidine (Spd). Rats were orally administered 0.5 ml of NaCl solution (0.9%) containing or not containing 400 micrograms.ml-1 of PGE2 twice daily, during three or ten days. Half an hour after the 18th ingestion of PGE2, 0.5 ml of NaCl solution (0.9%) containing MTX (16 mg.ml-1) was injected intravenously. Rats were killed exactly 48 hours after this injection. MTX had no effect on the Put content, increased the AMPc content and decreased the contents of DNA, proteins, Spm, Spd, PGE2 and sucrase or maltase activity. PGE2 had no effect on the biochemical parameters we studied, except on the contents of DNA (10-day treatment) and of PGE2 (3- and 10-day treatment). When MTX was injected after PGE2 treatment, as compared with what was observed when MTX was used as reported above, we observed--an increase in spermine content after 3-day PGE2 treatment and- an increase in the contents of DNA, Spm, Spd and disaccharidase activity after 10-day PGE2 treatment. No other significant variation in the other biochemical parameters was recorded, whatever the duration of the PGE2 treatment. These results indicate that PGE2 could partially protect the intestinal mucosa against the biochemical effects of MTX. Other experimental conditions may need to be chosen in order to obtain a better cytoprotective effect of PGE.

Induction of ornithine decarboxylase in adult rat hippocampal slices

Several factors involved in the regulation of ornithine decarboxylase (ODC) activity in adult rat brain tissue have been identified by using the in vitro hippocampal slice preparation. The same amino acids that have previously been reported to induce ODC in tissue culture, i.e., asparagine and glutamine, were found to produce a concentration- and time-dependent increase in ODC activity that reached a 100 fold the control value after 6 h of incubation. The effect of asparagine was totally blocked by inhibition of either protein or RNA synthesis, suggesting that the inducing amino acids increase ODC activity by stimulating the transcription of genes directly or indirectly regulating ODC activity. The effect of the inducing amino acids was potentiated by a variety of factors which by themselves did not modify ODC activity. In particular, opioid peptides markedly potentiated the effect of asparagine. Although the opiate antagonists naloxone and naltrexone totally blocked the effects of the opioid peptides on ODC induction, they also produced an inhibition of the asparagine-mediated increase in ODC activity. Other factors like dibutyryl cyclic AMP and insulin also potentiated the effects of asparagine on ODC activity. These results provide the first description of ODC induction in an in vitro preparation of adult brain tissue and indicate that the hippocampal slice preparation could be used to study the molecular mechanisms which regulate the expression and activity of ODC in the adult central nervous system. Moreover the data suggest possible mechanisms which may be involved in the induction of ODC in hippocampus by seizure activity.

Growth factors and intestinal neoplasms

Signals that control normal and neoplastic epithelial proliferation are not completely understood. We have reviewed the importance of the possible roles of the following control mechanisms: polyamine biosynthesis, intraluminal nutrients, gastrointestinal hormones and growth factors, bowel resection, carcinogens, and oncogenes. The mechanisms by which these agents act and the precise roles they play in normal and abnormal proliferation of intestinal mucosa have not yet been clearly defined. Peptide hormones and growth factors exert their mitogenic effects by first interacting with specific receptors in the cell membrane. Oncogenes induce production of growth factors or replace growth factors and, by themselves, stimulate growth. We believe that no single agent is likely to be responsible; rather, multiple agents are involved in stimulation of growth of normal and neoplastic intestinal epithelial cells. A clear understanding of the factors responsible for regulation of normal and abnormal intestinal cell growth will greatly facilitate the development of therapeutic strategies for the prevention and treatment of gastrointestinal cancers.

Ornithine decarboxylase and S-adenosylmethionine decarboxylase activity in the accessory sex organs of intact, castrated, and androgen-stimulated castrated rats

We have studied the activities of ornithine decarboxylase and adenosylmethionine decarboxylase in the 10(6)-m/s2 supernatants of the different lobes of the prostate and the seminal vesicles of castrates, androgen-stimulated castrates, and intact controls. After castration L-ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase (AMDC) activities fell in all tissues examined. The induction of kinetics was followed for 72 h after administration of testosterone propionate to castrated rats. AMDC activities increased more rapidly than ODC activities in every tissue studied. Peak activities were reached more rapidly in the dorsal lobe than in the other tissues. ODC activity of the ventral lobe increased linearly for 48 h after stimulation. In the other tissues studied, ODC activity reached a maximum after 24 h and thereafter leveled off or decreased. In conclusion we have found distinct differences in ODC and AMDC activity in various tissues and major differences between treatment groups, with near extinction of activity at castration. In castrates stimulated with testosterone, the between-group differences prevailed but with different patterns of ODC versus AMDC activity. AMDC is seemingly rate-limiting in polyamine synthesis in stimulated tissues, while ODC controls synthesis in tissues from castrated rats.

Changes in protein turnover in hypertrophying plantaris muscles of rats: effect of fenbufen--an inhibitor of prostaglandin synthesis

Plantaris muscle of the right hind limb of rats was subjected to hypertrophic stimulus by section of the tendons of the right gastrocnemius muscle. The RNA and protein content and the fractional rate of protein synthesis were elevated both 3 and 7 days after operation compared both with the unoperated left limb and with sham-operated control rats. The rate of protein degradation, calculated from the difference between the fractional rates of protein synthesis and protein gain of the muscles, was elevated in the plantaris 3-7 days after tenotomy. Dietary administration of the drug fenbufen reduced the RNA content and the ratio of RNA:protein in muscles from control animals. In one group of tenotomised rats administration of fenbufen commenced 3 days before tenotomy and resulted in a reduction in the ratio RNA:protein of the muscles of the left limb 3 days after the operation. Four days later, i.e. 7 days after tenotomy, both the ratio RNA:protein and the fractional rate of protein synthesis were significantly reduced in the fenbufen treated rats. In spite of these effects, fenbufen did not impair the ability of the plantaris to hypertrophy since the drug also reduced the rate of protein degradation.

Inhibition of ornithine decarboxylase activity by follicle stimulating hormone in primary culture of rat Sertoli cells

The effect of follicle stimulating hormone on the activity of ornithine decarboxylase (ODC) was determined in primary culture of rat Sertoli cells. Three different FSH preparations (NIH oFSH-S-15, S-16, and eFSH) inhibited ODC activity in rat Sertoli cells under different media conditions. The inhibition was both time- and dose-dependent. The mechanism of the FSH inhibitory effect was studied using dibutyryl cyclic adenosine monophosphate (dbcAMP), 1-methyl-3-isobutylxanthine (MIX), forskolin, and isoproterenol. All of these agents, known to elevate cellular cAMP levels, inhibited ODC activity in cultured rat Sertoli cells. The combined effect of each of these substances plus FSH was either greater than, or equal to, that of FSH alone, and was not additive. Dibutyryl cyclic guanosine monophosphate had no effect on the ODC activity. These findings suggest that FSH inhibition of ODC activity in the rat Sertoli cell may be mediated by cAMP.

Control of blastema cell proliferation by possible interplay of calcium and cyclic nucleotides during newt limb regeneration

The effects of the divalent cation ionophore A23187, papaverine, and chlorpromazine on the mitotic index and cyclic nucleotide levels in newt limb regeneration blastemata (Notophthalmus viridescens) were assessed. The results of the experiments suggest that an intracellular increase in divalent cation (Ca2+) concentration results in elevated cGMP levels, suppressed cAMP levels, and a corresponding increase in blastema cell proliferation. The results also suggest that the converse conditions, namely, calcium efflux or inhibition of calmodulin activation (i.e., inhibition of Ca2+ binding), yields elevated cAMP levels, suppressed cGMP levels, and a corresponding decrease in blastema cell divisions.

Induction of ornithine decarboxylase activity in mouse tissues by phorbol ester is effectively blocked by methylglyoxal bis(butylamidinohydrazone)

Ornithine decarboxylase (ODC) was induced in the liver, lung and brain of the mouse injected intraperitoneally with 12-O-tetradecanoylphorbol 13-acetate (TPA), showing maximal enzyme activity four hours after the injection. The increase of ODC activity was due to the enhanced syntheses of mRNA and protein. The induction of ODC activity by TPA was specifically blocked by methylglyoxal bis(butylamidinohydrazone) (MGBB), a competitive inhibitor of ODC and S-adenosylmethionine decarboxylase, but not by the analog methylglyoxal bis(guanylhydrazone) (MGBG).

Functional consequences of prenatal methylmercury exposure: effects on renal and hepatic responses to trophic stimuli and on renal excretory mechanisms

The effects of prenatal exposure to methylmercury on the functional development of renal and hepatic response systems was examined in the developing rat. Methylmercury produced an elevation of basal activity of renal ornithine decarboxylase (ODC, an enzyme involved in regulation of cellular maturation) and an eventual relative hypertrophy; liver ODC was reduced and hypertrophy was not evident. In contrast, the reactivity of liver ODC to trophic stimulants (vasopressin, isoproterenol) was markedly enhanced by prenatal methylmercury exposure, whereas renal ODC responses were much less affected (vasopressin) or actually reduced (isoproterenol). Targeted actions of methylmercury on renal excretory function were also prominent, with increased fractional excretions of urea and electrolytes and an eventual reduction in glomerular filtration as assessed by creatinine clearance. In addition, the reactivity of the kidney to challenge with desmopressin was altered coincidentally with the appearance of the effects on basal clearance mechanisms. These studies show that doses of methylmercury ordinarily associated with selective actions on development of neurobehavioral patterns also influence the functional ontogeny of other organ systems; furthermore, the fact that the target tissues are different for prenatal vs. postnatal methylmercury exposure, indicates that the functional teratology of methylmercury exhibits critical periods of sensitivity.

Effects of neonatal methylmercury exposure on adrenergic receptor binding sites in peripheral tissues of the developing rat

Neonatal exposure to methylmercury produces changes in patterns of tissue growth and function, in part, due to alterations in adrenergic neuronal input. To explore the mechanisms by which these changes come about, newborn rats were exposed to methylmercury (1 or 2.5 mg/kg per day) throughout the preweaning stage and the ontogeny of adrenergic receptor binding sites evaluated in liver, kidney, heart and lung, using [3H]prazosin (alpha 1-receptors), [3H]rauwolscine (alpha 2-receptors) and [125I]pindolol (beta-receptors). In the kidney, methylmercury caused decreases in beta- and alpha 1-receptor binding and increases in alpha 2-binding; previous work has shown that beta-receptor-mediated responses are generally enhanced in methylmercury-exposed pups, and the down-regulation of beta-receptor binding thus probably represents a compensatory action secondary to alterations in post-receptor coupling mechanisms. The effects of methylmercury on hepatic adrenergic receptors were different from those seen in the kidney, with substantial elevations in beta- and alpha 1-receptor binding apparent in the preweaning stage; this agrees also with the differences in effects of the mercurial on trophic reactivity and growth in the 2 tissues. Despite the fact that methylmercury causes activation of neonatal cardiac sympathetic nerves, beta-receptor binding sites in the heart were unaffected by methylmercury exposure; the failure to down-regulate cardiac postsynaptic receptors in the face of increased nerve activity again represents an anomaly of synaptic regulatory function. These results indicate that methylmercury alters adrenergic responsiveness, in part, through actions on the development of receptor binding sites, and further, that the organ-specificity and receptor subtype-selectivity are consistent with subsequent effects of the organomercurial on adrenergic participation in target organ growth; however, changes in receptor binding alone do not account for all of the effects of methylmercury on synaptic activity or trophic responses.

Induction of mouse epidermal ornithine decarboxylase by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate: dependence on calcium availability

The role of calcium in epidermal ornithine decarboxylase (ODC) induction by 12-O-tetradecanoylphorbol-13-acetate (TPA) was determined in adult mouse skin pieces incubated in serum-free minimal essential medium (MEM). Addition of TPA to skin pieces incubated in serum-free MEM, which contains 1.82 mM Ca2+ and 0.83 mM Mg2+, resulted in about a 200-fold increase in epidermal ODC activity at about 8 h after TPA treatment. TPA failed to induce epidermal ODC in skin pieces incubated in calcium-free medium. Similarly, chelation of extracellular calcium by ethyleneglycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) prevented ODC induction by TPA, which could be resumed upon calcium restoration in the medium. Furthermore, calcium ionophore A23187, which facilitates efflux of Ca2+ across cellular membranes, induced ODC activity in incubated skin pieces. Epidermal ODC activity increased by TPA appears to be the result of an increase in both the amount of ODC protein and the level of hybridizable ODC messenger. Inhibition of the induction of ODC activity by EGTA was the result of the inhibition of the amount of active ODC protein and the level of ODC mRNA.

Association of increased polyamine levels with isoproterenol-stimulated mucin secretion in the rat submandibular gland

Incubation of rat submandibular gland slices with 50 microM isoproterenol for 10-40 min stimulated mucin secretion and induced a 3- to 4-fold increase in tissue concentrations of the polyamines putrescine, spermidine and spermine. alpha-Difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, suppressed the isoproterenol-induced increase in submandibular polyamines and inhibited mucin secretion. Exogenous putrescine restored tissue polyamine levels and partially reversed the inhibitory effect of alpha-difluoromethylornithine on mucin secretion. Rapid increases in polyamine levels appear to mediate isoproterenol-stimulated mucin secretion in the rat submandibular gland.

Catecholamine-induced cardiac hypertrophy in a denervated, hemodynamically non-stressed heart transplant

Studies of stress-induced cardiac hypertrophy suggest that myocardial mass is regulated by the circulating level of epinephrine. The trophic effect is mediated by cardiac beta-adrenergic receptors, and in the murine, rat, and dog heart, specifically by beta 2-adrenergic receptors. The well-characterized functional effects of catecholamines on heart have obscured their role as myocardial trophic hormones. Therefore, we compared the effect of beta-adrenergic receptor stimulation on the myocardial mass of both a working innervated heart and an essentially nonworking denervated heterotopically transplanted heart in the same rat; in this model, the neural and stretch parameters are nonoperational in the transplanted heart. Ornithine decarboxylase (ODC), an enzyme elevated in a dose-dependent manner in heart by isoproterenol, was assayed in both hearts to determine the relationship between ODC activity and myocardial mass in response to isoproterenol administration in working, innervated heart compared to denervated, nonworking heart. In both recipient and donor heart, the myocardial mass paralleled the ability of an isoproterenol bolus to stimulate ODC in the respective heart. However, beta-adrenergic receptor activity in the donor heart was decreased 5 days after transplantation as assessed by the differential ability of a single dose of isoproterenol to stimulate ODC activity. Beta-receptor coupling to ODC activity in the donor heart exceeded that of the recipient heart at 10 days posttransplantation suggesting a time-dependent elevation of beta-adrenergic receptor activity in donor heart. At all times, alterations in myocardial mass paralleled beta-adrenoceptor activity as assessed by the ability of isoproterenol administration to elevate ODC activity. The results support the concept that myocardial mass is regulated by the level of circulating hormones, particularly epinephrine.

Epinephrine and norepinephrine syntheses are regulated by a glucocorticoid receptor-mediated mechanism in the bovine adrenal medulla

The bovine adrenal medulla was investigated regarding the presence of glucocorticoid binding protein and the increases in ornithine decarboxylase (ODC) activity and epinephrine and norepinephrine by dexamethasone. Scatchard analysis of specific cytosol [3H] dexamethasone-binding study indicated a single class of high affinity (kd, 35 +/- 5 nM) and limited binding sites (150 +/- 26 fmoles/mg protein). Competition studies of various steroids indicated a high affinity for dexamethasone and hydrocortisone. Sedimentation in sucrose density gradients revealed a 7.3 S binding peak in the cytosol. Dexamethasone caused an increase in ornithine decarboxylase (ODC) activity within 1 to 2 hours after which the norepinephrine and epinephrine contents increased 16 hours after the peak of ODC activity in a dose dependent manner of dexamethasone in bovine adrenal medullary chromaffin cells in primary monolayer culture. These data suggest that the bovine adrenal medulla is a target organ of glucocorticoid hormone and that norepinephrine and epinephrine syntheses are regulated by a glucocorticoid receptor-mediated mechanism.

Polyamines and Nucleic Acids in Gestational Trophoblastic Tumors

To test the relationship between tumor malignancy and content and distribution of polyamines and nucleic acids, 2 forms of human gestational trophoblastic tumors were examined: the hydatidiform mole (self-limited form) and the human choriocarcinoma (invasive form) xenografted into nude mice. The results indicate that there are 2 significant differences between the choriocarcinoma and the mole: 1) the choriocarcinoma is characterized by increased polyamine and nucleic acid levels, 2) the 2 tissues differ in their putrescine:spermidine and spermidine:spermine ratios. There is an increase in polyamines in the urine of mole-bearing patients over that of normal controls. The correlation between putrescine and spermidine with the chorionic gonadotropin indicates that these 2 polyamines reflect the biological activity of the mole.

Developmental changes in chromatin of skeletal muscle of rats: acetylation of chromosomal proteins and transcription

In vivo acetylation of chromosomal proteins and RNA synthesis were studied in the skeletal muscle of 3-30 day old developing rats. The levels of acetylated histones and nonhistone chromosomal (NHC) proteins are high at day 3 and decrease as development progresses. Spermine has no significant effect on acetylation. Incorporation of 3H-Uridine into RNA of both nuclear and cytoplasmic fractions is also maximum at day 3 and plateaus by day 14. Nuclear RNA synthesis following acetylation of chromosomal proteins is greatly stimulated in all the ages studied, whereas that in cytoplasmic RNA occurs only in 3 day old rats. Such modifications during early development may bring about conformational and functional changes in the chromatin and contribute significantly to the process of terminal differentiation of skeletal muscle cells.

Deviations in ornithine-related metabolism during hexachlorocyclohexane-induced hepatocarcinogenesis in mice: evidence for conversion of glutamate to ornithine

Chronic administration of technical-grade hexachlorocyclohexane in Swiss male mice resulted in necrosis, and later in adenomatous nodules and hepatocellular carcinomas at 3, 7, and 10 months, respectively, after initiation of the experiment. A definite pattern of changes were observed of arginase, ornithine transaminase, ornithine carbamoyltransferase activities, and metabolites related to ornithine. Conversion of glutamate to ornithine correlated well with the decreased glutamate and constant ornithine in liver of mice fed hexachlorocyclohexane for 7 months.

Putrescine has analgesic activity, in rats

Putrescine, intraperitoneally injected into rats at doses of 200, 300 and 400 mg/Kg, had a dose-dependent analgesic effect (hot plate, 55.5 degrees C), which was not antagonized by naloxone. Analgesia was also obtained by intracerebroventricular injection (1,000 nmoles/rat). Chronic administration (300 mg/Kg/day i.p. for 8 consecutive days) resulted in the development of tolerance. In our experimental conditions, no obvious toxicity was observed. These results may suggest for polyamines a role in nociception, and may disclose a new class of analgesic drugs.

Ornithine decarboxylase inhibitors and fetal growth retardation in mice

Putrescine (PUT) and the putrescine analogues, 1,3-diaminopropane (DAP) and 1,6-diaminohexane (DAH), were administered to pregnant female mice during the time of maximal fetal ornithine decarboxylase (ODC) activity, days 10-14 of gestation. Such treatment resulted in an inhibition of fetal ODC activity, as measured 2 hours later, and a proportional decrease in fetal weight, as measured on day 18 of gestation. The order of effectiveness for these compounds was DAP greater than DAH greater than PUT. Neither DAP nor DAH nor PUT were fetocidal nor maternally lethal under the treatment regimen employed. The generality of the effect of these compounds, i.e., the retardation of fetal growth and the lack of gross malformations, is consistent with the hypothesis that they are interfering with a primary process, probably protein synthesis. The restricted time span of effectiveness implies that these compounds are specific inhibitors of ODC and that decreased ODC activity is producing an effect on growth.

Induction by chloroform of two forms of ornithine decarboxylase in rat liver. Half-life of isozymes

Ornithine decarboxylase (ODC) in rat liver was separated into two species by DEAE-Sepharose CL-6B column chromatography. The activity of both species of ODC was increased at least 20-fold by chloroform treatment of the rats. The major species, Peak A, contained 65% of the ODC activity and possessed a half-life of 11 min. The second species, Peak B, accounted for 35% of the activity and possessed a half-life of 50 min. The long-lived species of ODC activity, induced in rat liver by chloroform, has not been reported previously and might be related to the prolonged induction of ODC activity by chloroform and to tumor promotion and growth.

Sulindac for polyposis of the colon

Four members of a Gardner's syndrome family had rectal and colon polyposis treated with nonsteroid anti-inflammatory drugs. Three of these patients had had subtotal colectomy and ileoproctostomy and the residual polyps arose in the rectal mucosa. The polyps almost completely disappeared when sulindac was administered. Indomethacin therapy over the course of a preceding year was ineffective in one of these patients. One patient (case 4) had diffuse polyposis in an intact colon. After sulindac therapy for a year, only three small mucosal polyps could be identified by air contrast barium enema and colonoscopic examination. These observations confirm those of Pollard and Luckert [1,2] on rats with chemically induced polyposis of the intestinal tract.

Effects of cyclic nucleotides on ornithine decarboxylase activity in mammary gland explants from mid-pregnant mice

Dibutyryl cAMP and prolactin stimulated ornithine decarboxylase activity in mouse mammary gland explants which had been preincubated with insulin and cortisol for 1 day; maximally stimulatory concentrations of dibutyryl cAMP and prolactin produced a response which was greater than the sum of the responses of prolactin and dibutyryl cAMP when tested alone. 8-Bromo-cGMP inhibited ornithine decarboxylase activity whereas other derivatives of cyclic nucleotides were without effect. Cortisol concentrations were found to be important for optimizing the dibutyryl cAMP and prolactin responses. Optimal prolactin responses were obtained with cortisol concentrations greater than 10(-7) M, whereas optimal dibutyryl cAMP responses were observed with cortisol concentrations less than 10(-7) M. Despite the differing optimal cortisol concentrations for the prolactin and dibutyryl cAMP responses, it is concluded that prolactin and dibutyryl cAMP probably stimulate ornithine decarboxylase activity in the mammary gland via the same mechanism.

Binding of epidermal growth factor in rat pancreatic acini

Specific, saturable EGF receptors were demonstrated in isolated rat pancreatic acini. Binding of EGF to these receptors was one-half maximal at 20 min and maximal at 120 min. Scatchard analyses revealed a single order of binding sites with a Kd of 4.90 nM. Following binding, EGF was rapidly internalized and converted to two acidic species. EGF did not alter either basal amylase release or the rate of [3H]phenylalanine incorporation into TCA-precipitable protein. The finding of high affinity EGF receptors in pancreatic acinar cells supports the hypothesis that EGF participates in the long-term regulation of pancreatic exocrine function.

Polyamine levels and diamine oxidase activity in hypertrophic heart of spontaneously hypertensive rats and of rats treated with isoproterenol

Polyamine levels and diamine oxidase (EC 1.4.3.6) activity were studied in hypertrophic heart of spontaneously hypertensive rats as well as in the heart of Wistar rats during the development and regression of cardiac hypertrophy induced by isoproterenol administration. In spontaneously hypertensive rats, putrescine content and diamine oxidase activity were higher than those found in normotensive Kyoto-Wistar control rats. During the development of cardiac hypertrophy induced by isoproterenol, there was an increase in polyamine content and diamine oxidase activity. The administration of cycloheximide or actinomycin D prevented the increase in diamine oxidase activity during the first 24 h after isoproterenol administration, demonstrating that the rise in diamine oxidase activity was due to synthesis of new enzyme. Following the cessation of isoproterenol treatment, cardiac hypertrophy regressed and polyamine levels and diamine oxidase activity diminished toward control values. The administration of aminoguanidine to isoproterenol-treated rats caused in the heart an inhibition of diamine oxidase activity that led to an increase in putrescine level beyond the values found in animals given isoproterenol alone. The results suggest that the enhancement of diamine oxidase activity plays a role in the regulation of putrescine level in hypertrophic heart.

Ornithine decarboxylase may be a multifunctional protein

Ornithine decarboxylase may undergo posttranslational modifications which alter its function. Both transamidation of glutamine residues in the enzyme catalyzed by TGase and phosphorylation of serine and threonine residues catalyzed by a polyamine-stimulated protein kinase have been demonstrated. Data are presented which suggest that these modifications result in translocation of the modified protein to the nucleolus where it regulates the activity of RNA polymerase I to transcribe rDNA, the only active nucleolar genes. Transamidation of specific proteins with primary amines catalyzed by intracellular TGase may be an important posttranslational modification, capable of altering genetic transcription. The rapid half-life of ODC (10-15 min) may be related to rapid posttranslational modification with loss of enzymatic activity rather than to protein degradation.

Calcium binding proteins and cellular regulation

An important feature of cellular regulation is the precise control of intracellular calcium levels. This is accomplished both by dynamic organelle release and sequestration of calcium and by specific calcium active transport mechanisms located in the plasma membrane. The actual calcium signal for mediation of a cellular response is carried out by specific intracellular proteins, the most widely studied examples are calmodulin and troponin C. The recent discovery of phospholipid protein kinase and calcimedins suggests receptor mediation via several independent proteins. The physiological importance of a particular protein as a calcium messenger rests on several features: 1) calcium binding is of the order of 1-10 microns, 2) the protein is known to be localized at the site of proposed action, 3) if translocation occurs upon activation, the time required is consistent with the time course of the physiologic response and 4) substrates or effectors at the next level of action when isolated can be demonstrated to have similar activation kinetics as in situ.

Independent induction and inhibition of ornithine decarboxylase and aryl hydrocarbon hydroxylase activities in rat epidermis

Changes in the activities of ornithine decarboxylase (ODC) and aryl hydrocarbon hydroxylase (AHH) were investigated in rat epidermis after wounding the skin and application of 7,12-dimethylbenz(a)anthracene (DMBA), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and several enzyme inhibitors. Wounding of the skin by vigorous shaving led to a marked induction of ODC activity with a peak at 6 hr. Topical application of a single dose of tetradecanoylphorbol-13-acetate to wounded skin did not affect the activities of ODC and AHH. Application of single large dose (2.5 mg) of DMBA increased AHH activity 7-fold without affecting ODC activity. DL-alpha-difluoromethyl ornithine, a specific irreversible inhibitor of ODC, almost completely abolished ODC activity but did not inhibit DMBA- or TCDD-induced AHH activity. Several potential modifiers, including retinoic acid, indomethacin, 1,3-diamino-2-propranol, alpha-naphthoflavone, and SKF 525 A had unequal effects on ODC and AHH activities. These data indicate that ODC and AHH induction processes in the epidermis are independent biochemical events that are not causally related.

Restoration by cyclic AMP of the differentiated phenotype of chondrocytes from de-differentiated cells pretreated with retinoids

Parathyroid hormone (PTH) increases the cyclic AMP level in rabbit costal chondrocytes in culture. PTH, dibutyryl cyclic AMP (DBcAMP), and 8-bromo cyclic AMP (8-Br cAMP)induce ornithine decarboxylase (ODC) and expression of the differentiated phenotype of chondrocytes in this cell system. On the other hand, retinoids inhibit expression of the differentiated phenotype of chondrocytes. In the present study, the effects of PTH, DBcAMP, and 8-Br cAMP on rabbit costal chondrocytes pretreated with retinoids were examined. PTH did not increase the cellular cyclic AMP level in de-differentiated cells that had been pretreated with retinyl acetate or retinoic acid for three days, but it did increase the cyclic AMP level four days after removal of retinoids. PTH did not stimulate ODC activity or expression of the differentiated phenotype of chondrocytes in the de-differentiated state. On the other hand, DBcAMP or 8-Br cAMP stimulated expression of the differentiated phenotype of chondrocytes even in de-differentiated cells, as judged by morphological and histological changes of the cells and increase in glycosaminoglycan synthesis. Cyclic AMP analogues also induced ODC in these cells.

Cyclic nucleotides in the denervated rat diaphragm and the effect of cyclic AMP on ornithine and adenosylmethionine decarboxylases

The concentrations of cyclic AMP and cyclic GMP were measured in the denervated rat diaphragm at various times following unilateral phrenicectomy. Cyclic AMP concentration was raised by the second day after operation, reached a peak by the third day, followed by another increase at around 10 days. By contrast, cyclic GMP concentration was decreased within a day after denervation and remained below control levels at all subsequent times studied. Epinephrine in vitro produced a comparable increase in the concentration of cyclic AMP in both normal and denervated tissue. The concentration of adenosine appeared unchanged in the denervated diaphragm by comparison with its innervated control. Activity of ornithine decarboxylase was elevated in the diaphragms of rats treated with dibutyryl cyclic AMP, but this effect could also be achieved with sodium butyrate alone. Adenosylmethionine decarboxylase activity, was unaffected after treatment with either compound. These observations and others discussed are taken to indicate a lack of direct relationship between cyclic AMP concentrations and the activity of the rate-limiting enzymes of polyamine biosynthesis in the rat diaphragm.